PROJECT SUMMARY Genotype directed therapy is the standard of care for patients with advanced non-small cell lung cancer (NSCLC). For patients with advanced epidermal growth factor receptor (EGFR) mutant, anaplastic lymphoma kinase (ALK) or ROS1 rearranged NSCLC, tyrosine kinase inhibitors (TKIs) are the standard of care initial systemic therapies. However, not all NSCLC patients harbor a targetable genomic alteration and even among those that can be initially treated with a TKI, acquired resistance inevitably develops. MET is a transmembrane receptor tyrosine kinase implicated in various aspects of malignancy including tumor growth, survival, invasion, migration, angiogenesis and metastasis. Aberrant alterations in the MET gene, leading to ligand (hepatocyte growth factor; HGF) independent activation of MET signaling, including mutations, copy number gains and rearrangements have been observed in many malignancies including in lung cancers. Several therapeutic strategies to inhibit MET signaling such as TKIs, antibodies targeting the MET receptor or HGF, have been developed and are undergoing clinical evaluation. As several clinical approaches to target MET in lung cancer have been unsuccessful as a result of selecting patients based on an ambivalent biomarker (MET immunohistochemistry (IHC); METMab) or using agents that were subsequently discovered not to be true MET inhibitors (Tivantinib (ARQ 197)), genomic alterations in MET have proven to be more reliable predictors of the clinical efficacy of MET inhibitors. In EGFR mutant NSCLC, MET amplification is a mechanism of acquired resistance to EGFR TKIs and the combination of EGFR and MET directed therapies is an effective therapeutic approach for such patients. De novo MET amplification and MET exon 14 skipping mutations have emerged as genomic alterations that predict for the clinical efficacy of single agent MET inhibitors. Intriguingly, some EGFR mutant MET amplified cancers also respond to single agent MET inhibition. The mechanistic basis for this is unknown. Of these different MET altered populations, MET exon 14 mutations are the most common (~ 3% of all lung adenocarcinomas) and multiple clinical trials are currently underway evaluating single agent MET TKIs in MET exon 14 mutant NSCLC. However, despite the clinical efficacy of MET TKIs in such cancers, acquired resistance will inevitably develop. Accordingly, we plan to investigate the mechanisms of acquired resistance to MET targeted therapies and determine whether drug resistant cancers retain their MET dependency. The mechanistic understanding of acquired drug resistance may help determine whether an alternative MET inhibitor (in the presence of a secondary MET mutation) or a combination (targeting a parallel or downstream signaling pathway) is likely to be therapeutically effective. We are accomplishing this through the following specific aims: Aim 1: To determine impact of MET mutations on efficacy of MET inhibitors; Aim 2: To understand how parallel or downstream pathway activation leads to MET inhibitor resistance; Aim 3:To determine mechanism of single agent MET inhibitor sensitivity in EGFR mutant cancers.